Manufacture of diphenylamine



Patented July 12, 1949 UNITED NT 2;476,1 Z

OF DIPHENYLAMINE Alexander 11. Widigr, Jr., Midland, 'Mich., "ass'ignor to ZlheDdw Chemical Company, Midland, lMic'h., 'a'coi-pl'iration-of Delaware 'NmDrauing. ilpplicatio'niluly I6, 1945, "Serial N 0. 605,458

*9 Claims. (Cl. 260-476) J This invention relates to-an-improvedprocess for the manufacture --of diphenylamine.

A known method for making diphenylamine involves the reaction of chlorobenzene with aniline in the presence of a-solid =alkali metal hy {1' .droxide, according to the-equation CeH5Cl+CHsNI-Iz-{ MOH(CHs)2NI-I+MC1H0 has I never seemedrindustrially ifeasible.

It has now been 'found that the rate :of .-reac- .tion of chlorobenzeneiand aniline in -.the,-presence 4 of sodium hydroxide, using .a tcuprous catalyst, may be materially increased by adding -a small proportion'of arpotassium com-pound to the re- .action mixture. With-this:additiomvreaction temperatures and times may be-lowered considerably; very acceptable yields .of diphenylamine may be realized-withoutexperiencingundueheating and equipment problems and without incurring the expense and 'trouble'occ'asioned by the use of powdered potassium hydroxide.

It has alsobeen found;coritrary to prior teaching, that the sodiumhydroxideneednotbe .added to the reaction mixture as a solid, vbutthat-. etpral and sometimes higher rates of reaction are realized when it is added as 'an aqueoussolution.

Theserfindings constitute-the basis of thepresent invention, which provides azsimple anmpracticable method for making diphenylamine on an industrial scale.

In carrying out the newxprocess, chlorobenzen'e, "aniline, cuprous oxide orza cuprous sa'lt fa's cat- :alyst, sodium hydroxide, and a small m'portion of a potassium compound .are charged into a closed vessel and heated to 'a're'ac'tion temperatureJusually atileast 200 C. Ellie mixtureii's then stirred and the water formed byftliereaeti'on is removed continuously, as by allowing it to vaporize and withdrawing the vapors. Chlorobenzene simultaneously vaporized is condensed and returned to the mixture. When the reaction has 2?. proceededtoa satisfactory extent; ordinarilyafter not .less than an hour, the mixture isreniovefl from :the wessel and treated to recover the diphenylami'ne.

The relative proportions of the reactants in-tlie process may "be varied widely, altholighitis liighly preferable thatboth thechlordb'enzene andthe aniIine be -present in 'stoit'zhiometric excess remtive '-i;o"=the so'dium hydroxide. "Ex'cess chlorob'n- -zene'itunctions as a carrierliquid in the removal of the water forme'd in the reaction, and excess aniline serves to minimize romance -of tar. Tf "desired, some carrier liquid other thanthefclilorobenzene reactant, e. 'g. "xy'lene, may be "added to assist in driving ofi-the-waterof the reaction by 'azeo'tropic" distillation.

While 'chlorob'enzene an'd "aniline wil1"'react"according to the invention in the "absence of '21 onprous catalyst, best results are obtained by addil'l'g' cuprous oxide or' a cuprous salt, efg. the i0 ilide. Alternatively, "the catalyst may be formed in situ by addi'n'g po'wd'ered copper or copper bronze to the reaction mixture. The catalyst should zordin'arily be added in a -proportio'n'-equiv alent to from 0.001 to 0.010 gram-'ato'mof copper per gram m'olbf sodium hydroxide.

The sodium hydroxide required in the reaction may be introduced as lumps, flakes, or powdered solid, or more conveniently as a concentrated aqueous solution, such as commercial 50percent caustic soda. When such a'solution isaddedQthe water "init vaporizes in the'early stages of the heating-step, leaving the sodium hydroxide in a ivery finely-divided and .unusuallyereactive state.

.-'In so far as is known, any .potassiumlcompound which is not adversely reactive with the other ireactants andproducts will.functionsatisfactoril-y ito :accelerate the formation of diphenylamine according to the invention. The simple iionizable inorganic potassium compounds, particularly the nhloridefl ydroxide, and carbonate, are-lmo'st-con- "verii'ent. These.ne'edno"t be specially purified,but may beadde'diinthe form of crude .mixtures with sodium eliloridejhydroxide, orearbonate, :such'as are "sometimes available asTby-products of chem-- 'ical industry. Only a small proportion of the pot'assium compound is required to obtain the accelerating effect, with a quantity equivalent to tfr'dm0i002 to 0.1 gram-atom of potassium per gram mol (if sodium hydroxide being generally suitable, and with at least 0.01 gram-atom being preferred.

The reaction of the invention proceeds at temperatures above about 200 C., the rate increasing rather sharply with increase in temperature.

3 Temperatures of 240 C. up to slightly below the fusing temperature of sodium hydroxide (318 0.), say to 315 C., are preferred, with optimum rates of reaction being obtained near 300 C. At these temperatures, it is necessary to operate in a closed vessel under pressure to maintain the reaction mixture in the liquid state, the pressure being created by vaporization of a part of the reactants or by introducing, at the start of reaction, a compressed inert gas, such as nitrogen or air.

The process is conveniently carried out in a stirring autoclave provided with heating coils and a reflux condenser fitted with a water trap. The desired reaction temperature is maintained by supplying heat to the coils, and the pressure is regulated, by admitting or venting inert gas, to a value such that the chlorobenzene or other carrier liquid present boils gently. The vapor thus formed enters the condenser, taking with it the water formed by the reaction and any water added with the sodium hydroxide. This water is retained in the trap, and the condensed chlorobenzene is returned continuously to the reacting mixture.

Reaction as described is continued until the desired proportion of diphenylamine has been formed, usually for at least an hour, even at 300 C., and more commonly for from 2 to hours. It is not essential that the reaction be carried strictly to completion; economic considerations may make it advantageous to withdraw the reaction mixture after a few hours, recover the diphenylamine, and return the unreacted materials for a second treatment.

The reaction mixture is worked up by diluting it with water to dissolve most of the inorganic substances present, filtering to remove solids, and allowing the filtrate to separate into two layers. The oily layer may then be subjected to fractional distillation, preferably at reduced pressureQthe excess chlorobenzene and aniline and the diphenylamine product being recovered as separate fractions of the distillate, leavin a small proportion of residual tar.

The following examples will illustrate the invention, but are not to be construed as limiting its scope.

Example 1 The reactants were charged into a stirring autoclave in the following relative proportions:

Gram mols Chlorobenzene 10.0 Aniline 31.9 Ground sodium hydroxide 5.07 Cuprous oxid 0.06 Potassium chloride 0.06

The mixture was stirred vigorously and heated to a temperature of 235 to 240 C. and the pressure in the autoclave was regulated at from 40 to 46 pounds per square inch gage. Heating was continued under these conditions for 10.0 hours, water and chlorobenzene distilling ofi continuously, and the latter being returned to the mixture. On cooling the mixture and working up the products, there was obtained 2.73 gram mole of diphenylamine. Analysis showed that 60 per cent of the sodium hydroxide initially added had been consumed.

4 Example 2 The reacants were mixed as follows:

Gram mols Chlorobenzene 12.5 Aniline 27.4 Sodium hydroxide (50 per cent aqueous solution) 10.3 Cuprous oxide 0.06 Potassium chloride 0.80

Reaction was carried out for 3.0 hours at a temperature of 295 to 300 C. under a pressure which was decreased gradually from 150 to pounds gage as the chlorobenzene was consumed. There was obtained 7.8 gram mols of diphenylamine.

What is claimed is:

1. In a process for making diphenylamine wherein chlorobenzene, aniline, and sodium hydroxide are heated together at a temperature of at least 200 C.,. the method of accelerating the reaction which comprises adding to the reaction mixture a small proportion of an ionizable inorganic potassium compound.

2. A process according to claim 1 wherein the potassium compound is potassium chloride.

3. A process according to claim 1 wherein the potassium compound is potassium hydroxide.

4. A process according to claim 1 wherein the potassium compound ispotassium carbonate.

5. A process for making diphenylamine which comprises agitating in a closed vessel a mixture of sodium hydroxide, chlorobenzene and aniline both in stoichiometric excess relative to the hydroxide, a cuprous catalyst in the proportion corresponding to from 0.001 to 0.01 gram-atom of copper per gram mol of the hydroxide, and a stable ionizable potassium compound in a proportion corresponding to from 0.002 to 0.1 gram atom of potassium per gram mol of the hydroxide, at a temperature of from 240 to 315 C. for a period of at least an hour while continuously removing from the reaction mixture the water liberated by the reaction, and thereafter recovering diphenylamine from the reaction mixture.

6. A process according to claim 5 wherein the potassium compound is potassium chloride.

7. A process according to claim 5 wherein the potassium compound is potassium hydroxide.

8. A process according to claim 5 wherein the potassium compound is potassium carbonate.

9. A process according to claim 5 wherein the sodium hydroxide is added as an aqueous solution.

ALEXANDER H. WIDIGER, JR.

REFERENCES CITED The following referenlces are of record in the file of this patent:

in Patent Oflice Library.) 

